The present invention is a method and ultrasonic device for modifying the physical properties of various workpiece materials through the use of ultrasonic energy.
Garments such as disposable diapers include elastic waist or leg bands. The bands are often constructed of an elastomeric material bonded to a backing material. The backing material is commonly referred to as a web or nonwoven fibrous material. The bonds are typically ultrasonic bonds or adhesive. One problem with a bonded elastomeric and web approach is that the web material is relatively inelastic compared to the elastomeric. As a result the elasticity of the material combination is limited.
The term xe2x80x9cUltrasonicxe2x80x9d generally refers to vibrations beyond the human audible sound frequencies. As employed herein, ultrasonic energy is defined as vibration energy above 16 kHz. Ultrasonic devices have been used for nondestructive testing, welding, cutting, and metal component cleaning. A sandwich type transducer driven by an electronic power supply, which is then amplified through a horn, is a common source of ultrasonic energy.
Ultrasonic energy is used to bond numerous materials. One example for bonding an elastomeric material to a web backing material is U.S. Pat. No. 4,863,542, Oshefsky et al. Oshefsky attempts to solve the problem of decreased laminate elasticity by stretching the elastomeric prior to bonding it with an inelastic web. The Oshefsky method has limitations that remain unresolved. One limitation is the bunching up of the web material when the elastic retracts. Bunching occurs when a non-elastic web material is partially bonded to a stretched elastic. When the stretched elastomeric is released, it contracts. The bonded non-elastic web material is forced to contract with the elastomeric causing the unbonded web to bunch together.
A similar reduction in elasticity occurs when a web and elastic are adhesively laminated. For example, diapers use an elastic laminated between two other web materials, which greatly reduces the elastic capability of the underlying elastic. Various means have been used to recapture this elasticity including ring rolling the web prior to laminating, or, ultrasonically cutting the elastic. However, the recovery of the lost elasticity has remained relatively small. Ring rolling can also result in other undesirable manifestations including cuts in the laminated web structure, partial damage to the elastic, and degradation of the appearance of the laminate finish.
There is a need for a method for regaining the elasticity of an elastic and web laminate. Improvements in the physical properties for materials such as breathable films are also needed. An ultrasonic device that allows continuous ultrasonic treatment of a workpiece without the use of rotary ultrasonic equipment may also be desirable in certain applications.
The present invention addresses the deficiencies of the prior art by providing a method and apparatus to achieve material property changes in a workpiece with ultrasonic energy. The method includes providing a horn with a first set of activation teeth having a pitch. The horn is adapted to produce ultrasonic energy with a frequency and amplitude. An anvil is provided with a second set of activation teeth having a pitch. The second set of activation teeth is disposed opposite the first set of activation teeth. The workpiece is placed between the first set of activation teeth and the second set of activation teeth. The first set of activation teeth and the second set of activation teeth mesh with each other, thereby engaging the workpiece with a depth of engagement and a clearance. The clearance combined with the depth of engagement between opposing sets of activation teeth allows the workpiece to be placed in tension between adjacent tooth tips. Ultrasonic energy is applied to the first set of activation teeth.
The ultrasonic device includes a horn with a first set of activation teeth having a pitch, height and length. The horn is adapted to produce ultrasonic energy with a frequency and amplitude. The ultrasonic device also includes an anvil with a second set of activation teeth having a pitch, height and length. The second set of activation teeth is disposed opposite and parallel to the first set of activation teeth. The two sets of activation teeth have an increasing tooth depth of engagement that progressively increases in a longitudinal direction creating a region of lesser tooth engagement and a region of greater tooth engagement.